Guidelines for estimating damage to hearing from exposure to noise have been promulgated by, among others, the National Institute of Occupational Safety and Health, the Environmental Protection Agency, and the International Organization for Standardization (ISO). The most recent guidelines are to be found in ISO Standard 1999.2, dated 1989. These documents have implications for the setting of tolerable limits for exposure to industrial noise that differ significantly from one to the other. However, there are reasons to believe that certain significant errors were present in analyses of some of the data that served as the basis for ISO 1999.2. One objective of this project is to identify and clarify any experimental errors and methodological problems in the studies used in the development of these guidelines. Predicting from pure-tone hearing levels a person's ability to understand speech in real life is of critical importance to the definition of what constitutes a significant degree of noise-induced hearing loss and, in turn, the setting of limits of exposure to noise. The relation between pure-tone thresholds and speech intelligibility tests, and between these measures and the ability of persons to satisfactorily understand speech in everyday life, are matters of controversy. The U.S. Public Health Service (USPHS) administered pure-tone threshold, sentence intelligibility, and hearing-ability rating data constitute a rich source of information on these matters that is not yet fully analyzed. The speech-test and hearing-ability rating data constitute a rich source of information on these matters. A second objective of the proposed project is, through analyses of the USPHS data, to further develop procedures for estimating, from pure-tone hearing levels, the ability of persons with hearing loss to understand sentence tests and to understand speech in real life.